1. Field of the Invention
The present invention relates to a semiconductor laser device and, more particularly, to a distributed feedback semiconductor laser device and a method for manufacturing that device which has a ridge waveguide structure with a predetermined ridge width formed on a principal plane of a semiconductor base.
2. Background Art
A distributed feedback semiconductor laser device having a ridge waveguide structure formed on a principal plane of a semiconductor base is discussed illustratively in 1998 IEEE Photonics Technology Letters, Vol. 10, No. 12, pp. 1688-1690.
This type of semiconductor laser device, capable of concentrating generated light within a ridge waveguide structure, is counted on to play a major role in optical communication applications from now on. The device is characterized by its diffraction grating formed not only inside the ridge waveguide structure but also outside of it. The characteristic makes it difficult to increase a coupling constant xcexa in effect between the generated light and the diffraction grating, which prevents optical output from getting sufficiently large. Furthermore, because of its poor controllability in the coupling constant and wavelength involved, the distributed feedback semiconductor laser device tends to suffer from wavelength variations in optical output.
It is therefore an object of the present invention to overcome the above and other deficiencies of the prior art and to provide an improved distributed feedback semiconductor laser device capable of boosting its optical output and stabilizing its wavelength.
It is another object of the present invention to provide a method for manufacturing an improved distributed feedback semiconductor laser device capable of boosting its optical output and stabilizing its wavelength.
According to one aspect of the present invention, a distributed feedback laser device comprises a semiconductor base having a ridge waveguide structure projecting from a principal plane thereof, the semiconductor base including a plurality of semiconductor layers for emitting light and a diffraction grating layer resonating with the emitted light, the ridge waveguide structure extending with a predetermined width from one edge of the semiconductor base to an opposite edge thereof, the diffraction grating layer being formed confined within the ridge waveguide structure having the predetermined width.
According to the invention, a distributed feedback laser device may be manufactured so that its diffraction grating layer is confined within the ridge waveguide structure. This permits enlarging of the coupling constant in effect between emitted light and the grating layer, thus boosting optical output and ensuring wavelength stabilization.
According to another aspect of the present invention, in a method of manufacturing a distributed feedback laser device, a plurality of semiconductor layers for emitting light are formed on a semiconductor substrate firstly. A diffraction grating layer having a plurality of grating elements arranged within a predetermined width is formed on the plurality of semiconductor layers secondly. Thirdly a ridge waveguide structure having the plurality of grating elements is formed through an etching process, the plurality of grating elements left confined in the ridge waveguide structure.
The manufacturing method involves first forming a diffraction grating layer having a plurality of grating elements arranged within a predetermined width. So that a ridge waveguide structure may then be formed in such a manner that the diffraction grating layer is left confined inside the ridge structure.
Other and further objects, features and advantages of the invention will appear more fully from the following description.